The technique traditionally used in the field of aeronautics to measure the aerodynamic flow along a wall consists in the observation of wool or nylon filaments called “tufts” stuck to the wall at one of their ends. However, these “tufts” can have an inherent instability with no direct link to the characteristics of the flow. Accordingly, in order to remedy these drawbacks, the “tufts” have been progressively replaced by plastic material “flow cones”. A flow cone is rigid, thin and light in weight and can be attached to the wall by a nylon filament at the level of the apex of the cone. Its lightness allows it to move freely and to align itself with the direction of the flow of the air.
Accordingly, in order to measure the aerodynamic flow over an aircraft, flow cones are installed in areas of the aircraft where the analyses are required. Because of their lightness the flow cones exhibit characteristic movements according to the type of aeronautical flow and the shape of which enables visualization in a video recording. These flow cones are filmed by onboard video cameras the recordings from which enable use of the data in real time or off-line.
However, this technique does not make it possible to study masked areas where it is difficult or even impossible to install the instrumentation, such as on the underside of the aircraft, for example. Moreover, it does not make it possible to measure accurately the direction of the flow over the wall and therefore does not make it possible to obtain an objective criterion as to the state of the flow.
For a more global characterization of the aerodynamic flow over an aircraft, NASA has developed a technique of injection of a fluid containing a tracer and a solvent during a stable phase of the flight. The rubbing at the wall will entrain this fluid along lines the geometry of which depends on the conditions of flow. The evaporation of the solvent while the flight conditions are maintained constant (for one to two minutes) will allow the tracer to be fixed. Once on the ground all the necessary observations may be made. This technique is described by D. Fisher et al. in the document entitled “In flight flow visualisation characteristics of the NASA F18 high Alpha research vehicle at high angle of attack”, NASA technical memo 4193, May 1990.
However, the technique of injection of and drying of a tracer in flight does not provide access to a real time visualization of the flow and moreover makes it possible to characterize only one test point per flight.
An object of the present disclosure is therefore to remedy the aforementioned drawbacks by an accurate air flow measuring device and a system for global measurement in real time of the aerodynamic flow over a wall at the same time as making it possible to carry out the measurement over all the areas of a wall and in a recurrent manner.